1. Field of the Invention
This invention relates to a film bonding method, a film bonding apparatus, and a semiconductor device manufacturing method, and more particularly to a film bonding method and a film bonding apparatus for use in bonding a die bond film to a semiconductor substrate (wafer), and a semiconductor device manufacturing method including a step of bonding a die bond film.
2. Description of the Related Art
In the manufacture of a semiconductor IC (Integrated Circuit), normally, first, a surface (semiconductor element-forming surface) of a semiconductor substrate (wafer) subjected to a predetermined wafer process is covered with a surface protective tape, and then the back (rear) surface of the wafer is ground (back grinding process) to thereby reduce the thickness of the wafer.
After the back grinding process, the surface protective tape is peeled off the surface of the wafer, and a dicing tape is bonded to the back surface of the wafer. In this state, a singulation process is carried out on the wafer from the front surface side thereof, whereby a plurality of semiconductor elements (chips) are formed.
Then, the singulated chips are separated from the dicing tape, and a die bonding process is performed on a predetermined portion of a semiconductor element-receiving container.
Conventionally, in the die bonding process, as a method of bonding chips to a support substrate, such as a lead frame, there has been widely employed a method in which first, an adhesive is coated on the surface of the support substrate, and then a chip is secured to the support substrate using the adhesive.
In recent years, however, a method is also used in which an adhesive film (die bond film) for securing semiconductor elements is bonded to the back surface of a wafer subjected to a back grinding process, and then the wafer is singulated.
According to this method, a singulated chip can be secured to a support substrate via a die bond film which is small and uniform in thickness and is bonded to the back surfaces of the chip, and therefore it is possible not only to secure the chip to a predetermined position with accuracy but also to further reduce the thickness (height) of the chip.
The above-described die bond film includes die bond films which have adhesive properties at normal temperature, or thermoplastic die bond films which exhibit adhesive properties when heated. The thermoplastic die bond films are advantageous in that they are easy to handle during the manufacturing process.
FIG. 20 shows a conventional method of bonding a thermoplastic die bond film to a wafer.
In bonding a thermoplastic die bond film 100 to the back surface of a wafer 101, a bonding method is employed in which the wafer is heated from a surface thereof opposite to a surface (back surface) where the die bond film 100 is bonded, that is, from a front surface (semiconductor element-forming surface) of the wafer, and in this state, the die bond film 100 is pressed against the back surface (bonding surface) of the wafer by a rubber roller 103.
There is also proposed another method of bonding a thermoplastic die bond film, in which the die bond film is progressively bonded without heating the whole surface of the wafer but by heating only part of the surface where bonding is being performed.
For example, there have been proposed a method in which a die bond film is bonded to a wafer using a roller provided with a heating mechanism, and a method in which a table including a heating and cooling mechanism is used, and after placing a wafer on the table, the heating and cooling of the table is partially controlled depending on the position of a roller for pressing a die bond film toward the wafer (see Japanese Unexamined Patent Publication No. 2004-186240).
Recently, it is necessary to make wafers even thinner in accordance with an increasing demand for further reduction of the size and thickness of semiconductor devices, and accordingly, there is an increasing demand for making the thickness of wafers not larger than 100 mμ.
As described above, generally, wafers are processed to a small thickness by back grinding after forming semiconductor elements. It is natural, however, that a thin wafer is low in strength and hence easy to crack.
In contrast, for example, an attempt is being made to avoid breakage of a thinned wafer by placing the wafer on a protective substrate having a small hole formed in the center thereof, and performing a grinding process or transfer of the wafer while fixedly sucking the wafer via the small hole (see Japanese Unexamined Patent Publication No. 2004-153193).
When the conventional die bond film-bonding method in general use is employed, that is, the method of performing back grinding of the back surface of a semiconductor substrate (wafer) after bonding a surface protective tape to the main surface of the wafer, and then bonding a die bond film to the back surface of the wafer while heating the whole surface of the wafer is employed, relatively large thermal expansion or thermal contraction occurs on the surface protective tape.
As a result, it is impossible for a thinned wafer having a thickness of approximately 100 mμ or less to bear such thermal deformation of the surface protective tape. This leads to cracking of the wafer.